sel4-kernel-loader

Kernel loader

sel4-kernel-loader is simlar in purpose to the upstream elfloader. The main practical difference is how it fits into a build system, allowing for different approaches to distribution and integration. elfloader is a C program built using CMake and depends on the kernel+application payload at link-time. sel4-kernel-loader itself is just the loader without the payload, and thus does not depend on the payload at build time. Instead, it is accompanied by a CLI component called sel4-kernel-loader-add-payload which is used to append the payload to the sel4-kernel-loader ELF image in a seperate preparation phase.

sel4-kernel-loader does, however, depend on the seL4 kernel at compile time. The kernel provided at build time is only used for computing addresses for memory layout. A different kernel can be provided to the CLI during the preparation phase, as long as that kernel's physical address range's start address is the same as that of the kernel provided at boot, and that kernel's physical address range's end address is no greater than that of the kernel provided at boot.

sel4-kernel-loader also depends on the libsel4 headers. These are provided in the same way as they are for the sel4-config crate and its dependants (i.e. via SEL4_PREFIX or SEL4_INCLUDE_DIRS).

Here is an example of how to build and use this crate. First, independantly of the application, build the loader and accompanying CLI tool:

CC=aarch64-linux-gnu-gcc \
SEL4_PREFIX=$my_sel4_prefix \
    cargo build \
        -Z build-std=core,alloc,compiler_builtins \
        -Z build-std-features=compiler-builtins-mem \
        --target aarch64-unknown-none \
        --release \
        -p sel4-kernel-loader

Later, prepare the loader by adding the kernel+application payload:

cargo run -p sel4-kernel-loader-add-payload -- \
    --sel4-prefix $my_sel4_prefix \
    --loader target/aarch64-unknown-none/release/sel4-kernel-loader \
    --app $my_app \
    -o image.elf

There are other ways to acquire and build this code. For example, one could use cargo install without having to clone this repository:

url="https://github.com/seL4/rust-sel4"

CC=aarch64-linux-gnu-gcc \
SEL4_PREFIX=$my_sel4_prefix \
    cargo install \
        -Z unstable-options \
        -Z build-std=core,alloc,compiler_builtins \
        -Z build-std-features=compiler-builtins-mem \
        --target aarch64-unknown-none \
        --release \
        --root $my_project_local_cargo_root \
        --git $url \
        sel4-kernel-loader

cargo install \
    --root $my_project_local_cargo_root \
    --git $url \
    sel4-kernel-loader-add-payload

$my_project_local_cargo_root/bin/sel4-kernel-loader-add-payload \
    --sel4-prefix $my_sel4_prefix \
    --loader $my_project_local_cargo_root/bin/sel4-kernel-loader \
    --app $my_app \
    -o image.elf